Polo 6R braking thread (Mainly GTI/Diesel)

[gavs]

Ok, I've been planning on writing something up for a while for my fellow 6R owners out there in regards to brakes and braking, so from a couple of earlier posts I have written in other threads, I will try to compile it all in the one location.

So, to start with....

---------- Post added at 12:58 PM ---------- Previous post was at 12:51 PM ----------

Ok, now to try and explain the principles of braking using my simpelton knowledge

Brakes are heat generators. They do this to turn your kinetic (moving) energy into heat energy which gets dissipated into the atmosphere. How? Your pads creating friction against your rotors.

That's the simple answer. The biggest enemy of your brakes is heat. Because they are heat generators, the hotter they are initially, the less heat that they can dissipate, therefore it takes you longer to stop. This in turn affects your pads. If the pads have a heat limit of say, 300 degrees C, then after that temperature, you start getting a longer stopping distance because they are starting to break down and are no longer in their operating range, therefore you go to a higher temperature level in your pads. How does different brake fluid help? Well, there are 2 reasons:

1) Brake fluid, like any liquid, has a boiling point. Due to the heat generated by using your brakes, this heat in turn gets transmitted through your calipers, back into the fluid. Again using 350C as an example, if water boils at 100C, this example fluid boils at 360C and your pads are no longer in their optimum range at 350C. This means that they are hotter than this when you go to stop, elevating their temperature to 370C. Remember, the brake fluid boils at 360C, so it is now boiling and turning to vapour in your brake lines. The pressure which is generated in the system when you put your foot on the pedal is sufficient to pressurise the fluid which squeezes your calipers onto the rotors, but it is not enough to compress the gas (vapourised brake fluid) in your lines as gasses need much more pressure to be compressed. This results in a "long pedal" which you might have heard of before. After being boiled, your brake fluid is never the same again and will have a constantly decreasing boiling point.

2) Again, with the temperature, but from a different perspective. Brake fluid is hygroscopic, meaning it absorbs water and eventually as it reacts with air (it takes a fair while!) but it can break down into water. This is bad because as shown in the example above, if you have any water in the system (and it can seep in over time) it boils long before the fluid, but because water has gotten into the system, your brake fluid itself is breaking down into water, so just 1 drop in a sealed container can destroy the fluid. So, if you standard fluid boils at (again) 360C, yet a Race fluid boils at 800C, the amount of water that renders your 360C fluid useless wont render your 800C fluid useless for a longer period of time. Race fluid is also engineered to withstand more extreme heat loading and cycling so it is far less likely to break down as readily, hence the $30 price difference to standard Castrol Dot 4 stuff.

---------- Post added at 01:00 PM ---------- Previous post was at 12:58 PM ----------

That as far as I know is the fundamentals behind braking regarding disc brakes anyway, don't ask about drums because I have no idea! What about cross drilled and slotted rotors, cross drilled rotors, slotted rotors etc? Well, there are 3 fundamental thoughts behind this.

1) Cross drilled. The thought is that under braking, your pads produce gasses due to friction against the rotor, which they do, but to the levels that adversely affect your performance, you are really going to struggle to get to that point..... The drilled holes supposedly let this gas escape into the ventilated part of the rotor, yet remove surface area and weaken the rotor (have a close look at an old drilled rotor and notice the cracks around the holes...)
Slotted. Again, same principle to remove gasses from between pad and rotor, yet vent to the outsides of the rotor. Again, material is removed resulting in less surface area, but the rotor is not weakened as these slots are generally cast into the rotor.
Combo of both. Honestly, these rotors do both? Give me a break....

2)
This, is a brembo F1 brake disc, see any slots or holes?....... Brakes (as mentioned above) are to dissipate energy through heat. The greater swept area of the rotor in contact with the pad during braking, the greater amount of energy can be removed as heat. This is also another reason to go to a bigger diameter, they won't decrease your stopping distance, however they are able to dissipate more heat over a broader area, therefore you are less likely to generate heat-induced brake fade.

3) Now, as a designer, I have spoken with a few engineers and fellow designers in the automotive field in my time. The reason they give me for cross drilling/slotting rotors? It's a simple one, looks. Cross drilled rotors and slotted rotors look cool, it's as simple as that. One designer who works for the VW group said that when he was working on the 977 lineup of Porsche GT series 911s, the engineers designed the carbon ceramic brakes for them, but they looked hideous, so the decision was made to cross drill them, so they looked cool, like they were actually worth the $25,000 premium.

So, on that note,I will be sticking with the standard rotors, just upgrading the pads and fluid

I hope that helps you guys in making some decisions

---------- Post added at 01:18 PM ---------- Previous post was at 01:00 PM ----------

So, after all that, how about some info on brake lines and some common misconceptions.

Misconception 1: Braided brake lines decrease stopping distance.
Ah, no. Braided brake lines have the benefit of not having the same initial flex that a rubber one would have once the pressure of braking is introduced into the brake line. Rubber brake lines do indeed swell slightly once pressure is introduced, this is true but it doesn't increase your stopping distance. What braided lines do however, is increase pedal feel and feedback. This is awesome for those of us who like taking our vehicles for a good hard mountain run and we can feel the pressure change when fade starts setting in, but not on a 6R. Why? I'll get to that...

Misconception 2:
Braided brake lines increase braking performance.
Not really, again, it comes back to pedal feel, again also, somewhat irrelevent in a 6R. For the ever so slight chance of a teeny weeny increase in braking performance from buying braided brake lines, put it towrads better, stickier tyres for the front of the car. These alone will provide such a big improvement, you will laugh about the day you nearly wasted your money!




Ok, so why are certain things irrelevent on a 6R? Simple. Control module 03, 10 Adaptation, 09: 0, 1, 2

This code alone is what controls your braking. In the 6R, your braking system is 90% identical to any hydraulic braking system except for one thing, the brake pedal itself. It is connected to the braking system as normal but to generate brake pedal "feel" and application ratios of pedal pressure vs caliper clamping pressure, it is connected to a box full of 1's and 0's that sends coded signals to another box that controls the brake master cylinder. I have personally found that the only difference in brake feel that I can get is once the pads I have are up to their prefered operating temperature, but by "feel" I don't mean the feel through the pedal because that resistance doesn't really change (it's probably more a placebo effect), the feel I get is through the rate of deceleration and when a certain amount of pressure applied gets a better/worse result, depending on temperature.

SO, with that section of coding, 0 is the factory default for brake distribution, 1 is midly worse, 2 is windscreen-headbut material. It changes the amount of pressure that the master cylinder applies dependant on pedal travel. It basically removes any modulation of the pedal that you have to give maximum braking performance. Good on the track, probably not quite as good when you need to modulate, especially in peak hour traffic!

The next post will be in regard to upgrades. What you can / cant do, what some costs are, and hopefully some attempt at technical info